This invention arose from the need for measurement of very high temperatures (to 2,000.degree. C.) in very hostile environments. A typical application might be within the environment existing within a nuclear test bundle during a simulated loss of cooling accident. Loss of coolant accident tests are specified for discrete high temperature excursions for short time periods. Practical devices must be utilized to monitor temperatures that exist at various locations within nuclear fuel test bundles under such test conditions.
The purpose of the present device is to measure the highest temperature achieved at discrete locations that are being monitored during high temperature procedures. The device is adapted for measuring such temperatures at very high design temperature ranges within a system that is normally maintained at a substantially lower working temperature. For instance, in nuclear reactor tests where temperatures being monitored might range to 2000.degree. C., the normal temperature of a working reactor environment is maintained at or below 260.degree. C. There is a substantial difference between the normal working temperature and the elevated design temperature range within which measurement is required.